1. Field of the Invention
The present invention relates to a lens driving apparatus, used in an optical system of an optical device such as a camera, for changing its power and adjusting its focus.
2. Related Background Art
Conventionally known as a lens barrel, used in an optical system of an optical device such as a camera, for changing its power and adjusting its focus is one having four lens groups, all of which are attached to a frame expandable from the camera body, whereas the lens groups are appropriately moved in the optical axis direction by use of a cam mechanism so as to change the power and adjust the focus, as disclosed in Japanese Patent Application Laid-Open No. HEI 7-20369.
This lens barrel comprises a barrier blade, disposed in front of a taking optical system, for opening/closing an optical path; a lens driving mechanism for advancing/retracting a part of the taking optical system upon a focusing operation of the taking optical system; a barrier driving mechanism for opening/closing the barrier blade; a first transmission mechanism for transmitting a driving force of a driving source to the lens driving mechanism; and a second transmission mechanism for transmitting the driving force of the driving source to the barrier driving mechanism, in which the transmission of the driving force to the second transmission mechanism is switched via a clutch mechanism as appropriate. The switching of the clutch mechanism is carried out by utilizing a pivotal member, so as to enhance the space efficiency, thereby reducing the size of the camera.
In order to realize precise focus adjustment in such a lens barrel, however, it is preferred that the position of a moving lens group be detected directly so as to move this lens group accurately. For detecting the position of lens group, a position detecting sensor is necessary. If a position detecting sensor is installed, the lens barrel may increase its size, whereby the cost of parts may rise.
In order to overcome such a problem, it is an object of the present invention to provide a lens driving apparatus which can prevent the lens barrel from increasing its size and cost while making it possible to detect positions of movable lens groups.
In order to achieve such an object, the present invention provides a lens driving apparatus comprising a lens optical system in which a plurality of lens groups are disposed along an optical axis, at least one of the lens groups being a movable lens group; a moving body, movable in a direction of the optical axis together with the movable lens group, having a predetermined width in the direction of the optical axis; and detecting means for detecting passages of both end portions of the moving body in the optical axis direction.
In the lens driving apparatus in accordance with the present invention, the detecting means may be an optical detector.
The lens driving apparatus in accordance with the present invention may be configured such that the lens optical system is accommodated in a plurality of cylindrical bodies which are expandable in a multistage manner, whereas the movable lens group changes a wait position according to an expanded position of the cylindrical bodies.
In the present invention, the moving body has a predetermined width, and passages of its both ends are detected, whereby the moving position of the movable lens group can be detected each time when any of both end portions of the moving body passes the detecting position. As a consequence, two positions of the movable lens group can be detected by one detecting means and one moving body, which makes it unnecessary to provide a plurality of detecting means and moving bodies. Therefore, the size and cost of the lens driving apparatus can be reduced. Also, the size and cost of the lens barrel can be reduced.
Since the position of the movable lens group is detected at two locations, reference positions of the movable lens group can accurately be set at two locations. When wait positions of the movable lens group are set at two locations with reference to the two reference positions according to the state of expansion of the lens barrel, the amount of movement of the movable lens group upon focusing can be shortened. As a consequence, moving errors can be lowered, which enables accurate focusing. Also, time parallax (time delay) at the time of photographing can be reduced.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.